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$\begingroup$I don't know if English is your first language. It isn't mine. I don't get what exactly you meant to ask, and I'm not the only one lost. If you can, please ask someone with good English skills to help you to rewrite this - and use simple, well structured language, because many people here are not native speakers and you need extra care to make sure everyone will understand you properly.$\endgroup$
– MołotJan 6 '17 at 14:39

$\begingroup$Welcome to Worlding, Lonnie, I have re-edited your question & requested it be reopened. If my edit has introduced things that contradicts or misunderstands your original question, you can edit it or revert it back to your original format. Interesting idea: how someone like the Flash the world he's superspeeding through it.$\endgroup$
– a4androidJan 7 '17 at 9:27

$\begingroup$As the discussion of the "Speed Force" on the existing answer shows, this is heavily dependent on how you implement this. Note that the Flash operates in magical fashion. He doesn't cause sonic booms or relativistic fusion. He can grab people and change their momentum without snapping necks. The Flash is not possible in our universe. You need either different physics or magic. Either way, you need to explain how that operates.$\endgroup$
– BrythanJan 7 '17 at 13:14

$\begingroup$It would be just like the question. [on hold]$\endgroup$
– SnowlockkJan 9 '17 at 10:43

1 Answer
1

Bullet time until relativity applies, at which point everybody dies.

It's a matter of how fast he goes, for as long as speed remain within the bounds for normal Newtonian movement you get the Matrix bullet time effect, everyone else looks slow. However if he keeps accelerating to relativistic speeds he hits the xkcd relativistic baseball threshold slightly ahead of significant time dilation.

The ball is going so fast that everything else is practically stationary. Even the molecules in the air are stationary. Air molecules vibrate back and forth at a few hundred miles per hour, but the ball is moving through them at 600 million miles per hour. This means that as far as the ball is concerned, they’re just hanging there, frozen.

The ideas of aerodynamics don’t apply here. Normally, air would flow around anything moving through it. But the air molecules in front of this ball don’t have time to be jostled out of the way. The ball smacks into them so hard that the atoms in the air molecules actually fuse with the atoms in the ball’s surface. Each collision releases a burst of gamma rays and scattered particles.

These gamma rays and debris expand outward in a bubble centered on the pitcher’s mound. They start to tear apart the molecules in the air, ripping the electrons from the nuclei and turning the air in the stadium into an expanding bubble of incandescent plasma. The wall of this bubble approaches the batter at about the speed of light—only slightly ahead of the ball itself.

$\begingroup$+1 for the relativistic baseball. Note that interesting phenomena begin as soon as any part of the Flash becomes supersonic...$\endgroup$
– AlexPJan 6 '17 at 10:06

$\begingroup$@AlexP in the DC Comics superhero case, that is handwaived by the existance of the "Speed Force". Suggested video: how fast the flash is (spoiler: FTL)$\endgroup$
– MindwinJan 6 '17 at 10:36

$\begingroup$@Mindwin, the whole thing is handwaved by the speed force. Otherwise he'd kill everyone any time he moved too fast ;)$\endgroup$
– SeparatrixJan 9 '17 at 9:23